Catalyst and its use for the selective hydrodesulfurization of an olefin containing hydrocarbon feedstock

ABSTRACT

A catalyst and its use for selectively desulfurizing sulfur compounds present in an olefin-containing hydrocarbon feedstock to very low levels with minimal hydrogenation of olefins. The catalyst comprises an inorganic oxide substrate containing a nickel compound, a molybdenum compound and optionally a phosphorus compound, that is overlaid with a molybdenum compound and a cobalt compound. The catalyst is further characterized as having a bimodal pore size distribution with a large portion of its total pore volume contained in pores having a diameter less than 250 angstroms and in pores having a diameter greater than 1000 angstroms.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Non-Provisional applicationSer. No. 14/693,967, filed on Apr. 23, 2015 entitled A CATALYST AND ITSUSE FOR THE SELECTIVE HYDRODESULFURIZATION OF AN OLEFIN CONTAINTINGHYDROCARBON FEEDSTOCK, which claims priority from the U.S. ProvisionalApplication No. 61/987,047, filed on May 1, 2014, the entirety of whichis incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a catalyst and process for the selectivehydrodesulfurization of an olefin-containing hydrocarbon feedstock.

BACKGROUND

Gasoline regulations are increasingly creating a need to treat variousrefinery streams and products, for example, cracked gasoline blendingmaterial, including coker naphtha and gasoline from a catalytic crackingunit, to remove undesirable sulfur that is contained in such refinerystreams and products.

One means by which sulfur may be removed from hydrocarbon streams thatcontain olefin compounds is through the use of various known catalytichydroprocessing methods. A problem with the use of many conventionalcatalytic hydroprocessing methods is that they typically tend tohydrogenate the olefin compounds as well as the sulfur compoundscontained in the hydrocarbon feed stream being treated. When thehydrocarbon feed stream is to be used as a gasoline-blending component,usually the presence of the olefins is desirable due to their relativelyhigh-octane values and octane contribution to the gasoline pool.

Cracked gasoline blending material typically contains highconcentrations of high-octane olefin compounds as well as concentrationsof sulfur compounds. It is desirable to be able to catalyticallydesulfurize the cracked gasoline blending materials with a minimum ofhydrogenation of the olefins contained in them. Disclosed in the priorart are many types of hydroprocessing catalysts and processes, and theprior art even discloses processes for the selectivehydrodesulfurization of olefin containing hydrocarbon feedstocks.

U.S. Pat. No. 5,266,188 is one patent that discloses a process for theselective hydrotreating of a cracked naphtha using a catalyst comprisinga Group VIB metal component, a Group VIII metal component, a magnesiumcomponent, and an alkali metal component. The Group VIB metal componentis present in the catalyst in an amount in the range of from about 4 wt% to about 20 wt %, and the Group VIII metal component is present in therange of from about 0.5 wt % to about 10 wt %, both calculated as oxidesand based on the total catalyst weight. The preferred Group VIB metalsare molybdenum and tungsten with molybdenum being preferred among these,and the preferred Group VIII metals are cobalt and nickel with cobaltbeing preferred among these.

U.S. Pat. No. 5,686,375 discloses a hydroprocessing catalyst thatcontains an overlayer of a Group VIB metal (preferably molybdenum)component on a support comprising an underbedded Group VIII metal(preferably nickel) component combined with a porous refractory oxide.The catalyst typically contains greater than 3.0, preferably greaterthan 4.0, and most preferably greater than 4.5 weight percent of GroupVIII metal component (calculated as the monoxide) and greater than 10,and preferably greater than 17 weight percent of Group VIB metalcomponent (calculated as the trioxide). A preferred catalyst isessentially free of supported metal components other than molybdenum andunderbedded nickel. A most highly preferred embodiment of the catalystcontains above 3 weight percent of nickel components, includingunderbedded nickel components encompassing at least 4.5 weight percentof the support. The catalyst is used in hydroprocessing methods such asdesulfurization and denitrogenation, but there is no indication that theprocess is selective to desulfurization.

U.S. Patent Publication No. 2003/0183556 A1 discloses a process for theselective hydrodesulfurization of naphtha which uses a preferredcatalyst that comprises a MoO3 concentration of about 1 to 10 wt. %,preferably about 2 to 8 wt. %, and more preferably about 4 to 6 wt. %,based on the total weight of the catalyst, and a CoO concentration ofabout 0.1 to 5 wt. %, preferably about 0.5 to 4 wt. %, and morepreferably about 1 to 3 wt. % based on the total weight of the catalyst.The process includes blending a cracked naphtha feedstream that containssulfur with a substantially olefin free naphtha feedstream andselectively hydrodesulfurizing the blend in the presence of ahydrodesulfurizing catalyst.

U.S. Pat. Nos. 6,589,418; 6,126,814; and 6,013,598 discloses processesfor the selective hydrodesulfurization of an olefin-containing naphthafeedstock that use catalysts that are similar to those disclosed in U.S.Patent Publication No. 2003/0183556.

U.S. Pat. No. 5,286,373 discloses a process for selectivelyhydrodesulfurizing a naphtha feedstock having a high olefin content byusing a deactivated hydrotreating catalyst.

The deactivated hydrotreating catalyst is a hydrotreating catalyst thathas been deactivated by use or by other means, and it generally containsdeposits of coke. The hydrotreating catalyst typically includes Group VIand Group VIII metals, provided on a porous support. The preferred GroupVI metals include chromium, molybdenum and tungsten, and the preferredGroup VIII metals include cobalt and nickel. Additional metals or otherelements can be present, such as phosphorus, fluorine, titanium, boronand the like. The particularly preferred metals include cobalt andmolybdenum.

As may be seen from the above review of some of the prior art there isgreat interest in the development of processes that provide for theselective catalytic hydrodesulfurization of sulfur-containing naphtha orhydrocarbon feedstocks that boil in the gasoline boiling range andcontain high olefin contents. By the selective hydrodesulfurization ofthe sulfur without significant simultaneous hydrogenation of the olefinsthe loss in octane of the feedstock may be minimized; since, as notedabove, olefins tend to be high-octane components of certain gasolineblending components.

An objective of the present invention therefore is to provide a catalystand process for selectively desulfurizing a sulfur-containinghydrocarbon feedstock that has high olefin content.

BRIEF SUMMARY OF THE INVENTION

Thus, in accordance with the invention, provided is a selectivehydrodesulfurization catalyst comprising: a calcined catalyst particlemade by calcining a shaped particle of a mixture comprising an inorganicoxide support material, molybdenum trioxide, and a nickel compound toprovide a calcined shaped mixture; wherein the calcined shaped mixtureis further overlaid with a cobalt compound and a molybdenum compound andis subjected to a further calcination step to produce the calcinedcatalyst particle; the calcined catalyst particle being characterized byhaving a bimodal pore size distribution with at least 20% of the totalpore volume being in pores having a diameter less than 250 angstroms andat least 10% of the total pore volume being in pores having a diametergreater than 1000 angstroms. Generally, the total pore volume of theinventive catalyst will be greater than 0.4 cc/gram.

Preferably, the calcined catalyst particle in accordance with theinvention will have at least 30% of its total pore volume in poreshaving a diameter less than 250 angstroms and at least 15% of its totalpore volume in pores having a diameter greater than 1000 angstroms.Preferably, the total pore volume of the inventive catalyst will begreater than 0.5 cc/gram.

Even more preferably, the calcined catalyst particle in accordance withthe invention will have at least 40% of its total pore volume in poreshaving a diameter less 250 angstroms and at least 20% of its total porevolume in pores having a diameter greater than 1000 angstroms.

It is also preferred for the nickel component in the calcined catalystparticle to be incorporated into its catalyst as part of the calcinedmixture and for there to be a material absence of impregnated nickel inthe overlayer.

The present invention further provides a process for selectivelyhydrodesulfurizing sulfur compounds contained in an olefin-containinghydrocarbon feedstock with minimal hydrogenation of olefins, whichprocess comprises: contacting under selective hydrodesulfurizationconditions an olefin-containing hydrocarbon feedstock with a catalystcomprising: a calcined catalyst particle made by calcining a shapedparticle of a mixture comprising an inorganic oxide support material,molybdenum trioxide, and a nickel compound to provide a calcined shapedmixture; wherein the calcined shaped mixture is further overlaid with acobalt compound and a molybdenum compound and is subjected to a furthercalcination step to produce the calcined catalyst particle; the calcinedcatalyst particle being characterized by having a bimodal pore sizedistribution with at least 20% of its total pore volume being in poreshaving a diameter less than 250 angstroms and at least 10% of its totalpore volume being in pores having a diameter greater than 1000angstroms.

Preferably, the calcined catalyst particle employed in the process ofthe invention will have at least 30% of its total pore volume in poreshaving a diameter less than 250 angstroms, at least 15% of its totalpore volume in pores having a diameter greater than 1000 angstroms.Preferably, the total pore volume of the catalyst employed in theinventive process is greater than 0.5 cc/gram.

Even more preferably, the calcined catalyst particle employed in theprocess of the invention will have at least 40% of its total pore volumein pores having a diameter less than 250 angstroms, at least 20% of itstotal pore volume will be in pores having a diameter greater than 1000angstroms.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a catalyst and process for the selectivehydrodesulfurization of an olefin-containing hydrocarbon feedstock thathas a sulfur concentration. What is meant when referring herein to theselective hydrodesulfurization of a feedstock is that sulfur is removedfrom the feedstock by the catalytic hydrogenation of the sulfurcompounds, but with minimum simultaneous hydrogenation of the olefincompounds contained in the feedstock. Refinery cracked feedstocks, suchas cracked naphtha or gasoline, typically contain high concentrations ofolefins as well as sulfur compounds, and it is desirable to be able toselectively desulfurize such cracked feedstocks with a minimum of olefinsaturation.

The catalyst and process of the present invention are particularlysuitable for selectively desulfurizing hydrocarbon feedstocks that boilin the naphtha or gasoline boiling range, which is typically from about10° C. (50° F.) to about 232.2° F. (450° F.), and, preferably from about21° C. (70° F.) to about 221° C. (430° F.). More preferably, thehydrocarbon feedstock predominantly boils in the range of from 32° C.(90° F.) to 210° C. (410° F.).

Hydrocarbon feedstocks that may be selectively desulfurized inaccordance with the present invention will contain both olefin compoundsand sulfur compounds. The olefin content or concentration of thehydrocarbon feedstock treated in accordance with the present inventioncan be in the range of upwardly to about 60 weight percent (wt %) of thetotal weight of the hydrocarbon feedstock and usually at least 5 wt % ofthe total weight of the hydrocarbon feedstock. A typical olefin contentof the hydrocarbon feedstock is in the range of from 5 wt % to 55 wt %of the total weight of the hydrocarbon feedstock, and, more typically,the range is from 8 wt % to 50 wt %. It is contemplated, however, thatthe hydrocarbon feedstock treated in accordance with the presentinvention will have concentrations of olefin compounds exceeding 10 wt %and even exceeding 15 wt % or even 20 wt %.

Generally, the hydrocarbon feedstock is olefin-containing and can be acracked naphtha product such as products from catalytic or thermalcracking units including, for example, an FCC cracked naphtha productfrom a conventional fluid catalytic cracking unit, a coker naphtha fromeither a delayed coker unit or a fluid coker unit, a hydrocrackernaphtha and any combination of cracked naphtha products. The crackednaphtha product typically has a high concentration of olefin compoundsand may have an undesirably high concentration of sulfur compounds.

The olefin-containing hydrocarbon feedstock of the inventive process canhave a significant sulfur content or sulfur concentration that generallyis in the range of from about 0.005 weight percent, i.e., 50 parts permillion by weight (ppmw), to about 1 weight percent, i.e., 10,000 ppmw.More typically, the sulfur content is in the range of from 100 ppmw to5000 ppmw, and, most typically, from 300 ppmw to 4000 ppmw. The sulfurcompounds of the olefin-containing hydrocarbon feedstock include organicsulfur compounds, such as, for example, disulfide compounds, thiolcompounds, thiophene compounds and benzothiophene compounds.

The olefin-containing hydrocarbon feedstock may also contain otherhydrocarbon compounds besides paraffin compounds and olefin compounds.The olefin-containing hydrocarbon feedstock may further comprisenaphthenes, and, further, comprise aromatics, and, further, compriseother unsaturated compounds, such as, open-chain and cyclic olefins,dienes, and cyclic hydrocarbons with olefinic side chains.

In one embodiment of the invention, an olefin-containing hydrocarbonfeedstock containing from about 2000 ppmw to 3000 ppmw of sulfurcompounds is hydrodesulfurized in a hydrotreating reactor down to asulfur concentration of from 100 ppmw to 300 ppmw. Thereafter, thesulfur concentration of the olefin-containing hydrocarbon feedstock isfurther reduced in another hydrotreating reactor, i.e., a “polishing” or“finishing” reactor”, down to a concentration of from 20 ppmw to 60 ppmwsulfur, preferably down to a concentration of less than 15 ppmw sulfur,and more preferably down to a concentration of 10 ppmw or less sulfur.

The inventive catalyst and process provides for the selective removal ofsulfur from an olefin-containing hydrocarbon feedstock, having a sulfurconcentration, by catalytic hydrodesulfurization. It is understoodherein that the references to hydrodesulfurization means that the sulfurcompounds of a feedstock are converted by the catalytic hydrogenation ofthe sulfur compounds to hydrogen sulfide which may then be removed toprovide a low sulfur product. It has been discovered that the use of aspecifically defined catalyst composition in the hydrodesulfurization ofthe olefin-containing hydrocarbon feedstock will provide forimprovements in the selective hydrodesulfurization of theolefin-containing hydrocarbon feedstocks as compared to the use ofconventional hydrodesulfurization catalysts.

A very important aspect of the selective hydrodesulfurization catalystof the present invention is its unique composition, especially withregard to the placement of the catalytically active metals in and on theshaped catalyst particle, and the unique bimodal pore structure of thecatalyst with a large percentage of pores having a diameter less than250 angstroms and a large percentage of pores with diameters over 1000angstroms, and in some embodiments even over 5000 angstroms.

The inventive selective hydrodesulfurization catalyst generallycomprises a calcined mixture made by calcining a formed (shaped)particle of a mixture comprising an inorganic oxide support material,molybdenum trioxide and a nickel compound. The calcined shaped mixtureor particle is then overlaid (preferably by impregnation) with a cobaltcompound and a further amount of a molybdenum compound and thensubjected to a second calcination step.

It is preferred for the nickel component of the inventive catalyst beincorporated into the shaped catalyst particle as underbedded nickel,and that there be a material absence of impregnated nickel on thesurface of the catalyst. It has been determined that the presence of amaterial amount of impregnated nickel on the surface of the catalyst hasthe effect of reducing its selectivity toward the desulfurization of anolefin-containing hydrocarbon feedstock; and, thus, it provides for anundesirable amount of olefin saturation. By “material absence ofimpregnated nickel on the surface of the catalyst” is meant that thereis less than 1.0 wt %, preferably less than 0.5 wt %, and mostpreferably less than 0.2 wt %, of impregnated nickel on the surface ofthe catalyst, calculated as the nickel being in the elemental form eventhough the nickel may be in another form.

While it is desirable to hold the amount of impregnated nickel on thesurface to levels below 1.0 wt %, it is understood that the inventivecatalyst may have a small concentration of non-impregnated nickel, e.g.,less than 0.1 wt %, preferably less than 0.5 wt % on the surface of thecatalyst as a result forming the shaped particle from a mixturecomprising an inorganic oxide support material, molybdenum trioxide anda nickel compound. However, the majority of the non-impregnated nickelwill be underbedded, i.e., uniformly dispersed in the inorganic oxidesupport material, while only a minor amount of the underbedded nickelwill be on the surface of the catalyst.

Another important feature of the inventive catalyst is its uniquebimodal pore structure including a relatively large percentage of thetotal pore volume in large pores having pore diameters exceeding 1000angstroms. In the inventive catalyst, at least 10%, preferably at least15%, and more preferably 20% of the total pore volume will be poreshaving diameters exceeding 1000 angstroms.

In one embodiment of the invention the unique bimodal pore structurewill, in addition to having a large percentage of the total pore volumein its pores with diameters exceeding 1000 angstroms, also contain arelatively large percentage of very large pores exceeding 5000angstroms. In this embodiment at least 5%, preferably at least 10%, andmore preferably at least 15%, of the total pore volume will be in poreshaving a diameter greater than 5000 angstroms.

Without wishing to be bound to any particular theory, it is believedthat bimodal pore structure and presence of a relatively high percentageof large diameter pores contributes to the outstanding selectivedesulfurization properties of the inventive catalyst; because, thepresence of the high amount of large pores results in shifting theavailable surface area so as to reduce the surface area within one rangeof pore diameters and increasing it in another. The presence of the highamount of large pores also reduces the diffusional resistance thatsulfur-containing aromatic species may have to being transported intothe catalyst interior. The presence of molybdenum and nickel in thecalcined shaped mixture, and molybdenum and cobalt in the overlayer,allow for removal of sulfur by direct desulfurization, thus reducingoverall hydrogenation and protecting a majority of olefin compounds fromhydrogenation.

References herein to total pore volume or pore size distribution are tothe pore volume or pore size distribution as determined using theStandard Test Method for Determining Pore Volume Distribution ofCatalysts by Mercury Intrusion Porosimetry, ASTM D4284-88, at a maximumpressure of 4000 bar, and a contact angle of 140°.

The porous refractory oxide of the catalyst composition can be anyrefractory oxide material that has the properties suitable for use asthe support component of the catalyst composition including the uniquebimodal pore structure. Examples of possible suitable porous refractoryoxide materials include silica, magnesia, silica-titania, zirconia,silica-zirconia, titania, silica-titania, alumina, silica-alumina, andalumino-silicate. The preferred porous refractory oxide is alumina. Thealumina can be in amorphous form or various crystalline forms, such as,alpha alumina, beta alumina, gamma alumina, delta alumina, eta alumina,theta alumina, boehmite, or mixtures thereof. Among the available formsof alumina, gamma alumina is most preferred.

As discussed above, an important feature of the inventive catalyst isits bimodal pore size distribution with a large percentage of pores withdiameters less than 250 angstroms, and large percentage of pores withdiameters greater than 1000 angstroms. The total pore volume of theinventive catalyst, as measured by standard mercury porosimetry methods,is in the range of from 0.4 cc/gram to 1.0 cc/gram. Preferably, thetotal pore volume is in the range of from 0.5 cc/gram to 0.9 cc/gram,and, most preferably, from 0.6 cc/gram to 0.8 cc/gram. The surface areaof the inventive catalyst, as measured by the B.E.T. method, generallyexceeds about 125 m²/gram, and it is typically in the range of fromabout 150 to about 250 m²/gram.

Another important aspect of the inventive catalyst, is that the nickelcontent should be substantially or completely in the form of underbeddednickel. Thus, the catalyst contains no material concentration ofimpregnated nickel in the overlayer, i.e., there is a material absenceof impregnated nickel in the overlayer. Thus, the step of impregnatingthe calcined shaped particle does not include the incorporation of anysignificant or material amount of nickel in the impregnating solution.

In one embodiment of the inventive catalyst there is no materialconcentration of cobalt incorporated into the support. In other wordsthere is no underbedded cobalt. Rather the cobalt component of thecatalyst is present in the form of a cobalt overlayer on the refractoryporous oxide support containing the underbedded molybdenum and nickelcomponents, and optionally a phosphorus component.

In yet another embodiment of the inventive catalyst, the molybdenumcontent of the catalyst is in the form of both underbedded molybdenumand an overlayer containing molybdenum.

It is also a feature of the inventive catalyst to further comprise aphosphorus component. This phosphorus component can be in the formeither as underbedded phosphorus or as an overlayer of phosphorus. In apreferred embodiment, the inventive catalyst contains phosphorus both inthe form of underbedded phosphorus and as an overlayer of phosphorus.

While the mechanism explaining why the inventive catalyst exhibitsparticularly good catalytic properties is not certain, it is believed,however, that the particular combination of features of the catalyst,some of which features are noted above, is what contributes to itsunique and unexpected selective hydrodesulfurization properties.

In the method for preparing the inventive catalyst two calcination stepsare used. The particle subjected to the first calcination step isprepared by combining the starting materials of the catalyst to form amixture. These starting materials include an inorganic oxide material, amolybdenum source, preferably molybdenum trioxide, and a nickel source.The inorganic oxide material, molybdenum source and nickel source forthe mixture may be provided in whole or in part from crushedhydrotreating or hydrocracking catalyst fines.

In certain embodiments of the invention a phosphorus source may also beincluded in the preparation of the mixture. The phosphorus source forthe mixture may also be provided in whole or part from crushed catalystfines.

If crushed catalyst fines are employed as the source of the inorganicoxide material, molybdenum, nickel and/or phosphorus, it is preferredfor the catalyst be crushed to yield a pore size distribution such thatthe median pore size diameter of the catalyst fines is under 100 μm, andpreferably, under 50 μm.

It is believed that the form of the molybdenum source employed in themixture contributes in some manner to the enhanced properties of theinventive catalyst. Therefore, it is preferred for the molybdenum sourcethat is mixed with the other starting materials of the mixture to be inthe form of molybdenum trioxide as opposed to, for example, a molybdenumsalt compound. It is further desirable for the molybdenum trioxide to bein the form of finely divided particles, that may be as a dry powder, oras particles in a suspension or slurry, or particles obtained fromcrushed hydrotreating or hydrocracking catalyst fines.

The inorganic oxide material is also generally in the form of a powderand is selected from the group consisting of alumina, silica, andalumina-silica.

The nickel source may be selected from any suitable source of nickelincluding nickel salt compounds, e.g., nickel nitrate, both dry anddissolved in solution, nickel oxide, or any other suitable nickelsource, including, for example from crushed catalyst fines.

The mixture is formed by any suitable method or means known to thoseskilled in the art, including, but not limited to, the use of suchvarious solids-mixing machines as tumblers, stationary shells ortroughs, muller mixers, which are either batch type of continuous type,and impact mixers, and the use of such suitable types of eitherbatch-wise or continuous mixers for mixing solids or liquids or for theformation of paste-like mixtures that are extrudable. Suitable types ofbatch mixtures include, but are not limited to, change-can mixers,stationary-tank mixers, double-arm kneading mixers that are equippedwith any suitable type of mixing blade. Suitable types of continuousmixers include, but are not limited to, single or double screwextruders, trough-and-screw mixers and pug mills.

The mixing of starting materials of the catalyst may be conducted duringany suitable time period necessary to properly homogenize the mixture.Generally, the blending time may be in the range of upwardly to 2 ormore than 3 hours. Typically, the blending time is in the range of from0.1 hours to 3 hours.

The term “co-mulling” is used broadly in this specification to mean thatat least the recited starting materials are mixed together to form amixture of the individual components of the mixture that is preferably asubstantially uniform or homogeneous mixture of the individualcomponents of such mixture. This term is intended to be broad enough inscope to include the mixing of the starting materials so as to yield apaste that exhibits properties making it capable of being extruded orformed into extrudate particles by any of the known extrusion methods.But, also, the term is intended to encompass the mixing of the startingmaterials so as to yield a mixture that is preferably substantiallyhomogeneous and capable of being agglomerated into formed particles(also referred to as “shaped” particles), such as, spheroids, pills ortablets, cylinders, irregular extrusions or merely loosely boundaggregates or clusters, by any of the methods known to those skilled inthe art, including, but not limited to, molding, tableting, pressing,pelletizing, extruding, and tumbling.

Once the starting materials of the catalyst are properly mixed,preferably by co-mulling, and formed into shaped particles, a dryingstep may advantageously be used for removing certain quantities of wateror volatiles that are included within the mixture or shaped particles.

The drying of the shaped particles may be conducted at any suitabletemperature for removing excess water or volatiles, but, preferably, thedrying temperature will be in the range of from about 75° C. to 250° C.

The time period for drying the particles is any suitable period of timenecessary to provide for the desired amount of reduction in the volatilecontent of the particles prior to the calcination step.

The dried or undried particles are calcined in the presence of anoxygen-containing fluid, such as air, at a temperature that is suitablefor achieving a desired degree of calcination. Generally, thecalcination temperature is in the range of from 1000° F. (538° C.) to1600° F. (871° C.), preferably between 1200° F. (649° C.) and 1500° F.(816° C.), and most preferably between 1250° F. (677° C.) and 1450° F.(788° C.).

Controlling the temperature conditions at which the mixture is calcinedcan be important to providing a calcined shaped particle having the porestructure properties described herein.

The amount of molybdenum that is co-mulled into the mixture should besuch as to provide in the calcined shaped particle a molybdenum contentin the range of from 1 weight percent (wt %) to about 9 wt % of thetotal weight of the calcined shaped particle, with the weight percentbeing based on the molybdenum as elemental metal. The calcined shapedparticle is the co-mulled mixture that has been agglomerated or formedinto a particle, e.g., extruded to form an extrudate, and that iscalcined to provide a calcined shaped particle as described above.

It is desirable for the calcined shaped particle to have from 2 wt % to7 wt % molybdenum; but, it is more desirable for the molybdenum contentto be from 3 wt % to 6 wt % of the calcined shaped particle, on anelemental basis. It is understood that a significant, if not major,portion of the total molybdenum content of the final calcined catalystparticle is present as an overlayer of molybdenum in addition to theunderbedded molybdenum.

The amount of nickel that is in the co-mulled mixture should be such asto provide in the calcined shaped particle a nickel content in the rangeof from or about 0.5 wt % to or about 2 wt % of the total weight of thecalcined shaped particle, with the weight percent being based on thenickel as elemental metal. However, it is desirable for the nickelcontent of the calcined shaped particle to be in the range of from 0.3wt % to 1 wt %, and, it is more desirable for the nickel content to bein the range of from 0.6 wt % to 0.9 wt % of the calcined shapedparticle. It is preferred that substantially all of the nickel contentof the inventive catalyst be in the form of underbedded nickel, and thatthere be no material amount, or the substantial absence, of overlaidnickel.

For the embodiments of the inventive catalyst which have a concentrationof phosphorus, the phosphorus may be present in the form of underbeddedphosphorus or as an overlayer of phosphorus, or as a combination of bothunderbedded phosphorus and phosphorus in the overlayer. The phosphorusmay be present in the calcined catalyst particle (the finished catalyst)in an amount in the range of from 0.1 wt % to 3.5 wt %, calculated asthe element. It is preferred for the phosphorus content of the calcinedcatalyst particle to be in the range of from 0.3 wt % to 2.5 wt %, and,most preferably, from 0.4 wt % to 1 wt %, calculated as the element.

The impregnation solution used to incorporate the overlayer of cobalt,molybdenum, and phosphorus, if present, into the calcined shapedparticle so as to provide the impregnated particle is prepared by mixingtogether and dissolving a cobalt source, a molybdenum source, and aphosphorus source in water. Slight heating of the mixture may be appliedas required to help in dissolving the components, and, if necessary, asuitable acid or base may be used to assist in the dissolution of thecomponents. The pH of the impregnating solution is not critical. Ifphosphoric acid is used as the source of phosphorus, the pH may berelatively low, e.g., less than 4. If a base is added to theimpregnating solution the pH may relatively high, e.g., above 8. In oneembodiment of the invention, the impregnation solution is a basesolution comprising a molybdenum source, a cobalt source and ammoniumhydroxide, the latter of which can be formed by adding ammonia to theaqueous impregnating solution.

Molybdenum compounds that may suitably be used in the preparation of theimpregnation solution include, but are not limited to, molybdenumtrioxide and ammonium molybdate. If molybdenum trioxide is employed inthe impregnating solution, it will typically be added with phosphoricacid and heated. If ammonium molybdate is employed in the impregnatingsolution, it typically will be added to a basic solution, e.g., aqueousammonium hydroxide.

The molybdenum concentration in the impregnation solution that isincorporated into the calcined particle should be such as to provide forthe final calcined catalyst particle having a molybdenum content in therange of from 9 wt % to 23 wt % (calculated as elemental metal), withthe weight percent being based on the total weight of the calcinedcatalyst particle. Preferably, the amount of molybdenum that iscontained in the impregnation solution to be such as to provide acalcined catalyst particle having a molybdenum content in the range offrom 12 wt % to 19 wt %, more preferably from 14 wt % to 18 wt %. It hasbeen surprisingly found that higher molybdenum concentrations in thecalcined catalyst particle, e.g., from 14 wt % to 18 wt %, calculated aselemental metal, actually helps to reduce olefin saturation instead ofincreasing it as would be expected.

Cobalt compounds suitable for use in the preparation of the impregnationsolution include, but are not limited to, cobalt hydroxide, cobaltnitrate, cobalt acetate, cobalt carbonate and cobalt oxide. Cobalt oxideand cobalt nitrate are the preferred cobalt compounds with cobalt oxidebeing the most preferred.

The amount of cobalt contained in the impregnation solution should besuch as to provide for a final calcined catalyst particle having acobalt content in the range of from 2 wt % to 8 wt %, calculated aselemental cobalt, with the weight percent being based on the totalweight of the calcined catalyst particle. However, it is desirable forthe amount of the cobalt compound that is contained in the impregnationsolution to be such as to provide for the calcined catalyst particlehaving cobalt content in the range of from 3 wt % to 7 wt %, preferably,from 3 wt % to 6 wt % and, most preferably, from 3 wt % to 5 wt %,calculated as elemental cobalt.

When a phosphorus compound is used in the impregnation solution, it istypically added as a salt compound of phosphorus or an oxyacid ofphosphorus. Suitable salt compounds include, but are not limited, tophosphate compounds with a cation such as sodium, potassium, rubidium,cesium, or ammonium, or any of the aqueous forms of phosphate (e.g.,phosphate ion (PO₄ ⁻³), hydrogen phosphate ion (HPO₄ ⁻²), dihydrogenphosphate ion (H₂PO⁻⁴) and trihydrogen phosphate (H₃PO₄)). Suitableoxyacids of phosphorus include but are not limited to phosphorus acid(H₃PO₃), phosphoric acid (H₃PO₄), hydrophosphorus acid (H₃PO₂).

The overlayer metals are preferably incorporated into the calcinedshaped particle by any impregnation procedure or method that suitablyprovides for the metal overlayer of cobalt and molybdenum and, ifapplied, phosphorus, at the concentrations as presented above and toprovide the impregnated particle. Suitable impregnation proceduresinclude, for example, spray impregnation, soaking, multi-dip procedures,and incipient wetness impregnation methods.

The impregnated particle is then dried to remove a portion of the freewater or other volatiles from the impregnated particle. The dryingtemperature is typically in the range of from 75° C. to 250° C. The timeperiod for drying the impregnated particle is any suitable period oftime necessary to provide for the desired amount of reduction in thevolatile content of the particles prior to calcination of theimpregnated particle.

The impregnated particle, which may or may not have been dried, iscalcined in the presence of an oxygen-containing fluid, such as air. Thetemperature at which the impregnated particle is calcined generally isin the range of from 371° C. (700° F.) to about 648° C. (1200° F.).Preferably, the calcination temperature is in the range of from 427° C.(800° F.) to about 648° C. (1200° F.), and, more preferably, it is inthe range of from 482° C. (900° F.) to 648° C. (1200° F.).

It has been found that the activity of the final catalyst is adverselyaffected if the impregnated shaped particle is calcined at highcalcination temperature, for example at temperatures of 700° C. (1300°F.) or above. Therefore, it is preferred for the calcination temperaturefor the impregnated particle not exceed 648° C. (1200° F.).

The length of time for conducting the calcination is that which isrequired to remove the volatile matter and convert the metal compoundsin the impregnated particle substantially into the metal oxide form. Thetime required for the calcination is generally in the range of fromabout 0.5 hours to about 4 hours.

The inventive selective hydrodesulfurization process includescontacting, under selective hydrodesulfurization conditions, anolefin-containing hydrocarbon feedstock as described herein with acatalyst composition as described herein, and, preferably, yielding alow sulfur product that has a sulfur concentration much reduced belowthe sulfur concentration of the olefin-containing hydrocarbon feedstock.

The inventive process can provide for a sulfur reduction in an amountgreater than 40 weight percent of the sulfur contained in theolefin-containing hydrocarbon feedstock while causing less than a 30percent bromine number reduction by the catalytic hydrogenation of theolefin compounds contained in the olefin-containing hydrocarbonfeedstock to yield the low sulfur product. The bromine number of anolefin-containing hydrocarbon feedstock can the determined by ASTMD-1159 and is a measure of double bonds, i.e., unsaturation, in thehydrocarbon feedstock.

While the sulfur reduction of at least 40 weight percent with less thana 30 percent bromine number reduction is a reasonably selectivehydrodesulfurization of an olefin-containing feedstock, it is desirablefor the process to be more selective in the hydodesulfurization of thefeedstock by providing for a higher percentage of sulfur reduction butwith a 30 percent or lower bromine number reduction. It is, thus,desirable for the desulfurization to provide for a sulfur reduction ofat least 50 weight percent and even at least 60 weight percent.Preferably, the sulfur reduction is at least 70 weight percent, and,more preferably, the sulfur reduction is at least 80 weight percent.Most preferably, the sulfur reduction is greater than 90 weight percent.

It is desirable for the bromine number reduction, which is a measure ofthe olefin reduction, be minimized Thus, it is desirable that thepercent bromine number reduction upon hydrogenation be less than 30weight percent. Preferably, the bromine number reduction is less than 25weight percent, and, most preferably, the bromine number reduction isless than 20 weight percent.

When referring herein to the “weight percent sulfur reduction” of thesulfur contained in the olefin-containing hydrocarbon feedstock, what ismeant is the difference between the weight percent of sulfur in thefeedstock and the weight percent of sulfur in the yielded product,divided by the weight of sulfur in the feedstock, multiplied by thenumber one-hundred (100).

When referring herein to “bromine number reduction” what is meant is thedifference between the bromine number of the olefin-containinghydrocarbon feedstock and the bromine number of the yielded product,divided by the bromine number of the olefin-containing hydrocarbonfeedstock, multiplied by the number one-hundred (100).

The selective hydrodesulfurization catalyst of the invention may beemployed as a part of any suitable reactor system that provides for thecontacting of the catalyst composition with the hydrocarbon feedstockunder suitable selective hydrodesulfurization reaction conditions thatcan include the presence of hydrogen and an elevated temperature andtotal pressure. Such suitable reactor systems can include fixed catalystbed systems, ebullating catalyst bed systems, slurried catalyst systems,and fluidized catalyst bed systems. The preferred reactor system is thatwhich includes a fixed bed of the catalyst composition contained withina reactor vessel equipped with a reactor feed inlet means, such as afeed inlet nozzle, for introducing the hydrocarbon feedstock into thereactor vessel, and a reactor effluent outlet means, such as an effluentoutlet nozzle, for withdrawing the reactor effluent or low sulfurproduct from the reactor vessel.

The selective hydrodesulfurization reaction temperature is generally inthe range of from about 232° C. (450° F.) to 343° C. (650° F.). Thepreferred selective hydrodesulfurization reaction temperature is in therange of from 249° C. (480° F.) to 316° C. (600° F.).

The inventive process generally operates at a selectivehydrodesulfurization reaction pressure in the range of from about 100psia to about 800 psia, preferably, from 150 psia to 600 psia, and, mostpreferably, from 200 psia to 400 psia.

The flow rate at which the olefin-containing hydrocarbon feedstock ischarged to the reaction zone of the inventive process is generally suchas to provide a liquid hourly space velocity (LHSV) in the range of from0.1 hr⁻¹ to 15 hr⁻¹. The term “liquid hourly space velocity”, as usedherein, means the numerical ratio of the rate at which the hydrocarbonfeedstock is charged to the reaction zone of the inventive process involume per hour divided by the volume of catalyst contained in thereaction zone to which the hydrocarbon feedstock is charged. Thepreferred LHSV is in the range of from 1 hr⁻¹ to 12 hr⁻¹, morepreferably, from 2 hr⁻¹ to 10 hr⁻¹.

The hydrogen treat gas rate is the amount of hydrogen charged toreaction zone of the present process together with the olefin-containinghydrocarbon feedstock. The amount of hydrogen relative to the amount ofhydrocarbon feedstock charged to the reaction zone may be in the rangeupwardly to about 1000 m³/m³ (cubic meter/cubic meter) which isequivalent to 5603 SCF/bbl (standard cubic feet/barrel). More typically,the amount of hydrogen relative to the amount of hydrocarbon feedstockis in the range of from 9 to 178 m³/m³ (50 to 1000 SCF/bbl). Thepreferred range for the hydrogen-to-hydrocarbon feedstock ratio is from18 to 36 m³/m³ (100 to 200 SCF/bbl).

The following examples are presented to further illustrate theinvention, but they are not to be construed as limiting the scope of theinvention.

Example 1

This Example 1 describes the preparation of Catalyst A in accordancewith the invention and the properties and characteristics of suchcatalyst. Catalyst A was prepared by first forming a shaped mixturewhich was calcined at a first calcination temperature to form a calcinedshaped particle. The calcined shaped particle was subsequentlyimpregnated with an impregnation solution containing additionalcatalytic metals forming an overlayer on the calcined shaped particle.The impregnated calcined shaped particle was then recalcined at a secondcalcination temperature to form a calcined catalyst particle, which isthe selective hyrodesulfurization catalyst composition of the invention.

Preparation of Calcined Shaped Particle

Several mixtures were prepared by mixing an alumina powder with finesfrom various crushed commercial hydroprocessing catalysts whichcontained molybdenum, nickel and phosphorus. The mixtures were mulledwith a 1% aqueous solution of nitric acid for 35 minutes, extruded into1.3 mm trilobe cylinders, dried at 100° C. (212° F.) for 3 hours toproduce shaped particles which were calcined at 677° C. (1250° F.) for 2hours. The resulting calcined shaped particles had from 4-5 wt %molybdenum, 0.7-1.0 wt % nickel and 0.5 to 1.0 wt % phosphorus. The poresize distribution of a representative calcined shaped particle, asdetermined by Hg intrusion under pressure, is shown in Table 1 below.

TABLE 1 Pore Volume Distribution: Total Pore Volume, cc/g 0.97 % PoreVolume in Pores Having Diameters: Less than 70 Å 4.4  70-100 Å 24.7100-130 Å 22.4 130-150 Å 4.7 150-180 Å 3.2 180-200 Å 1.3 200-240 Å 1.6240-300 Å 1.4 300-350 Å 0.7 350-450 Å 1.0 450-600 Å 0.8 600-1000 Å  1.4Greater than 1000 32.0Impregnation of the Calcined Shaped Particle

A calcined shaped particle prepared as described above was impregnatedwith an aqueous basic impregnating solution containing approximately 16w % molybdenum (added as ammonium heptamolybdate) and 4.3 w % cobalt(added as cobalt carbonate). The base employed in the impregnatingsolution was ammonium hydroxide. The impregnated calcined shapedparticle was allowed to age for two hours, dried at 125° C. overnight,and subjected to a further calcination at 900° F. (482° C.). The metalsconcentration, surface area and pore size distribution of the finalcalcined catalyst composition are shown in Table 2, below.

TABLE 2 Metals Concentration Mo, wt % 19.5 Co, wt % 4.2 Ni, wt % 0.8 P,wt % 0.9 Surface Area 168 m²/g Pore Volume Distribution: Total PoreVolume, cc/g 0.644 Median Pore Diameter, Å 124.8 % Pore Volume in PoresHaving Diameters:  70-100 Å 11.64 100-130 Å 28.09 130-150 Å 11.17150-200 Å 8.23 200-240 Å 2.17 240-300 Å 1.17 300-350 Å 0.78 350-450 Å1.40 450-600 Å 0.93 600-1000 Å  1.40 Greater than 1000 Å 31.66 Greaterthan 5000 Å 19.71Comparative Catalyst B

Catalyst B is a commercial hydrodesulfurization catalyst generally usedfor finishing or polishing reactor applications comprising 3.4 wt %cobalt and 13.6 wt % molybdenum on an alumina support and further havinga surface area of 235 m²/g. Catalyst B has 98% of its total pore volumein pores having a diameter less than 250 Å, and no measurable percentageof pores having a pore diameter of 1000 Å or greater.

Example 2

This Example 2 describes the experimental procedure used to measure theperformance of Catalyst A, in accordance with the invention, andComparative Catalyst B, in the selective hydrodesulfurization of anolefin-containing hydrocarbon feedstock (a catalytically crackedgasoline) having a concentration of sulfur.

A laboratory stainless steel isothermal tube reactor, having a nominaldiameter of ¾ inch, was packed with a volume of the relevant catalyst(either Catalyst A or Catalyst B). The catalyst was supported by a layer20 mesh silicon carbide and on top of the catalyst bed was placed alayer of 20 mesh silicon carbide. The catalyst was mixed in a 4:1 ratioof silicon carbide diluent to catalyst, and filled into the reactor insix equal aliquots, making sure that the catalyst was uniformlydistributed across the reactor bed. The catalyst was sulfided prior topassing the feed over it at hydrotreatment conditions. A catalyticallycracked gasoline feed, having a bromine number of 24, a total sulfurcontent of 159 ppm, an initial boiling point and a final boiling pointrespectively of 56.1° C. (133° F.) and 247.8° C. (478° F.), was passedover the catalyst at isothermal operating temperatures ranging from246.1° C. (475° F.) to 315.6° C. (600° F.), a liquid hourly spacevelocity (for hydrocarbon feed) of 10 hr⁻¹, a gaseous hourly spacevelocity (for hydrogen gas rate) of 200 SCF/bbl, and a pressure of 280psig for each of the reactor runs.

Presented in Table 3 is a summary of the results from the reactor runsdescribed above showing the amount of sulfur removal relative to theamount olefin saturation (as indicated by bromine number reduction) foreach of the reactor runs.

TABLE 3 Selective Desulfurization Test Results Bromine Sulfur NumberSulfur, Reduction, Bromine Reduction, Catalyst ppm % Number % Catalyst A18 88.7 18.3 23.8 (in accordance 14 91.2 17.3 27.9 with the invention)21 86.8 15.0 37.5 Catalyst B (Comparative) 20 87.4 13.0 45.8

The above presented data show that Catalyst A in accordance with theinvention, which has a unique bimodal pore structure and has molybdenumand nickel underbedded in an inorganic refractory oxide substrateoverlaid with molybdenum and cobalt, provides for a higher amount ofsulfur removal with a lower amount of olefin reduction (as reflected bythe lower bromine number reduction) relative to commercial Catalyst B.

It is understood that while particular embodiments of the invention havebeen described herein, reasonable variations, modifications andadaptations thereof may be made that are within the scope of thedescribed disclosure and the appended claims without departing from thescope of the invention as defined by the claims.

The invention claimed is:
 1. A process for selectively hydrodesulfurizing sulfur compounds contained in an olefin-containing hydrocarbon feedstock with minimal hydrogenation of olefins, which process comprises: contacting in a reactor under selective hydrodesulfurization conditions said olefin-containing hydrocarbon feedstock with a calcined catalyst particle made by calcining a shaped particle of a mixture comprising an inorganic oxide support material, molybdenum trioxide and a nickel compound to provide a calcined shaped particle; wherein said calcined shaped particle is further overlaid with a cobalt compound and a molybdenum compound and is subjected to a further calcination step to produce said calcined catalyst particle, said calcined catalyst particle being characterized by having a bimodal pore size distribution with at least 20% of the total pore volume being in pores having a diameter less than 250 angstroms and at least 10% of the total pore volume being in pores having a diameter greater than 1000 angstroms.
 2. The process as recited in claim 1, wherein said catalyst has a molybdenum content of from 9 wt % to 23 wt %, a cobalt content of from 2 wt % to 8 wt %, a nickel content of from 0.5 wt % to 2 wt %, and a phosphorus content of from 0.1 wt % to 3.5 wt %, each of said percentages calculated as the element.
 3. The process as recited in claim 2, wherein said olefin containing feedstock is a cracked gasoline or cracked naphtha feedstock.
 4. The process as recited in claim 3, wherein the reactor is a polishing reactor.
 5. The process as recited in claim 4, wherein the sulfur content of the cracked gasoline feedstock is reduced to below 15 ppmw.
 6. The process as recited in claim 5, wherein said calcined catalyst particle has at least 40% of the total pore volume in pores having a diameter less than 250 angstroms and at least 20% of the total pore volume in pores having a diameter greater than 1000 angstroms.
 7. The process as recited in claim 1, wherein said calcined catalyst particle has at least 30% of the total pore volume in pores having a diameter less than 250 angstroms and at least 15% of the total pore volume in pores having a diameter greater than 1000 angstroms.
 8. The process as recited in claim 1, wherein said calcined shaped particle is overlaid with a substantial absence of impregnated nickel.
 9. The process as recited in claim 1, wherein said calcined catalyst particle has at least 5% of the total pore volume in pores having a diameter greater than 5000 angstroms. 